It is well known that citrates and their salts are useful as emulsifying agents in the preparation of food products, for example, dairy products including process cheese. The preparation and properties of such emulsifying agents are well known. See, U.S. Pat. No. 2,485,637 (Gooding) and German Patent Nos. 938,581 and 934,632.
Sodium citrates are commonly used in the manufacture of process cheese either alone or in mixtures. The sodium citrates complex calcium ions in the cheese to solubilize the protein and increase its hydration and swelling, to facilitate emulsification of fat, impart flexibility to cheese slices and adjust and stabilize pH. (See, Caric et al., Food Microstructure, Vol. 4, pp. 297 (1985). Citrates are of great importance to cheese processing because they affect the chemical and physical properties of the finished cheese product. Sodium and potassium citrates are not emulsifiers in the strict sense, i.e. they are not surface-active substances, yet they are commonly included in the group of ingredients called "emulsifying agents". (See Caric et al., Food Microstructure, Vol. 4, pgs. 297-312 (1985).
Process cheese is prepared by heating hard cheese and/or soft cheese in a mixture with certain emulsifying agents in a melting process to a temperature above about 80.degree. C. During this melting process, the insoluble starting cheeses are converted into liquid by means of the emulsifying agents. (See U.S. Pat. No. 3,615,586).
The known processes to prepare process cheese typically involve the addition of the sodium citrate emulsifying agents as dry-solids or as a concentrated solution from separate heated storage tanks. Problems are associated with these processes, however. Adding solid sources of sodium citrates can result in a citrate build up within a cooker or blender because the solid citrates do not fully dissolve and stick to the augers. The build-up of citrates on the inside of the cooker or blender causes the cheese to burn during the cooking cycle. Undissolved citrates can also give the processed cheese a lumpy consistency. Furthermore, when a solid source of sodium citrate does not fully dissolve in the process mixture, the residual undissolved solid sodium citrate contributes to the solids that are removed by filters.
Alternatively, if a concentrated liquid source of sodium citrate is utilized in the cheese manufacturing process, this solution must be stored at elevated temperatures (120.degree. to 140.degree. F.) to prevent crystallization of the sodium citrates from solution. Storing the concentrated sodium citrate solution at elevated temperatures requires expensive insulating and heating equipment which increases manufacturing costs significantly. Furthermore, if a malfunction allows the temperature to drop, the solutions can crystallize within the delivery system, resulting in expensive downtime, repairs and/or replacement of the tanks, pumps, valves and piping.
Trisodium citrate, unlike phosphates, can be the subject of bacterial spoilage (See, Caric et al., Food Microstructure, Vol. 4, pp. 297 (1985). Solutions of sodium citrate have a pH of around 9.0, therefore, microbial proliferation can easily exist.
Sodium citrate is used in slice cheese primarily because of superior processability versus sodium phosphate. Particularly, slice cheese is subject to ribbon breakage in preparation during its travels over the chill rollers, as it is spread into thin sheets, cut and stacked. Citrates allow the slice cheese greater flexibility than sodium phosphates and is used for this purpose.
The addition of dry solid sources of citrates requires human labor to physically add the appropriate amount of the citrate. This results in substantial bag disposal cost, additions to landfills, and occasionally, human error in measuring the amount of citrate to be added. Injuries from lifting heavy bags are also a concern for employees and employers.
For these reasons, the preparation of process cheese using a dry solid source of sodium citrate or by adding separate amounts of concentrated sodium citrate solutions stored at elevated temperatures is an expensive process. The use of the solid has the same disadvantages as mentioned above for processing cheese. Also, the use of liquid sodium citrate would require heated storage and steam traced piping.
Solutions of trisodium citrate cannot exist above about 35 wt-% at standard temperature and pressure. Thus the use of such a solution is not practical for process cheese makers because the high moisture content exceeds the finished product's allowable moisture content. A process cheese manufacturer could, for example, switch from liquid cream to dry cream to make up for the added moisture from 35 wt-% sodium citrate, but they would lose the advantage of pumping liquid cream vis-a-vis manually handling dry material, and increasing overall costs.
Process cheese manufacturers could switch to a more soluble liquid potassium citrate, but "potassium citrate (K.sub.3 H.sub.5 C.sub.6 O.sub.7) is not suitable because it renders the finished product bitter in taste." (See Caric et al., Food Microstructure, Vol. 4, pp. 297 (1985).
A need exists for a way to use a liquid citrate product that is high in concentration, does not make the finished product bitter in taste, and does not require heated storage and delivery systems.
A two part citrate system where a liquid sodium citrate is mixed with a base sodium hydroxide 50% fulfills this need.